1. Field of the Invention
The present invention relates to a magnetoresistive element, and to a thin-film magnetic head, a head assembly and a magnetic disk drive each including the magnetoresistive element.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of magnetic disk drives has increased. A widely used type of thin-film magnetic head is a composite thin-film magnetic head that has a structure in which a write head having an induction-type electromagnetic transducer for writing and a read head having a magnetoresistive element (that may be hereinafter referred to as MR element) for reading are stacked on a substrate.
MR elements include GMR (giant magnetoresistive) elements utilizing a giant magnetoresistive effect, and TMR (tunneling magnetoresistive) elements utilizing a tunneling magnetoresistive effect.
Read heads are required to have characteristics of high sensitivity and high output. As the read heads that satisfy such requirements, those incorporating spin-valve GMR elements or TMR elements have been mass-produced.
Spin-valve GMR elements and TMR elements each typically include a free layer, a pinned layer, a spacer layer disposed between the free layer and the pinned layer, and an antiferromagnetic layer disposed on a side of the pinned layer farther from the spacer layer. The free layer is a ferromagnetic layer whose magnetization changes its direction in response to a signal magnetic field. The pinned layer is a ferromagnetic layer having a magnetization in a fixed direction. The antiferromagnetic layer is a layer that fixes the direction of the magnetization of the pinned layer by means of exchange coupling with the pinned layer. The spacer layer is a nonmagnetic conductive layer in spin-valve GMR elements, or is a tunnel barrier layer in TMR elements.
Read heads incorporating GMR elements include those having a CIP (current-in-plane) structure in which a current used for detecting a signal magnetic field (hereinafter referred to as a sense current) is fed in the direction parallel to the planes of the layers constituting the GMR element, and those having a CPP (current-perpendicular-to-plane) structure in which the sense current is fed in a direction intersecting the planes of the layers constituting the GMR element, such as the direction perpendicular to the planes of the layers constituting the GMR element. Read heads incorporating the TMR elements mentioned above are also of the CPP structure.
Read heads each have a pair of shields sandwiching the MR element. The distance between the two shields taken in a medium facing surface that faces toward a recording medium is called a read gap length. Recently, with an increase in recording density, there have been increasing demands for a reduction in track width and a reduction in read gap length in read heads.
In a typical configuration of an MR element having the free layer, the pinned layer, the spacer layer and the antiferromagnetic layer, an end face of each of the free layer, the pinned layer, the spacer layer and the antiferromagnetic layer is exposed at the medium facing surface. In the MR element having such a configuration, it is difficult to reduce the read gap length because the antiferromagnetic layer is relatively great in thickness.
As a technique enabling a reduction in read gap length in an MR element having the free layer, the pinned layer, the spacer layer and the antiferromagnetic layer, there is known one in which the antiferromagnetic layer is disposed away from the medium facing surface, as disclosed in JP 2005-44489A, JP 2004-335071A, JP 2005-346869A, and JP 2007-80904A, for example. According to this technique, an end face of the antiferromagnetic layer is not exposed at the medium facing surface and it is therefore possible to reduce the read gap length by a length equivalent to the thickness of the antiferromagnetic layer, compared with the case where an end face of the antiferromagnetic layer is exposed at the medium facing surface.
However, the above technique cannot respond to a demand for a further reduction in read gap length.